I'm looking for an overview of community developed software projects that people here actually use for their robotics needs. So what open source software do you use and (if informative) what do you use it for?

If you install ROS on a rasberry pie you can do so many things. ROS (Robotics Operating System) is an open source system that lets you perform high level and low level tasks and offers many packages that help you with your programming needs. For example if your robot has a camera then you may be able to use an open source ROS software package to take the input from your camera.